Crossing FAQ

The scientific inquiry, evaluation and planning that led to this design was quite extensive, and involves, and continues to involve, some of the top experts in the world on wildlife crossings along with input of the five main project partners: Caltrans, the National Park Service, the Santa Monica Mountains Conservancy/MRCA, Resource Conservation District of the Santa Monica Mountains, and the National Wildlife Federation.

A feasibility study by Caltrans was conducted in 2015 that evaluated other alternatives, and a crossing site assessment by experts from across the world was released in 2018 that reviewed potential sites along the 101 Freeway as part of a linkage analysis—the experts agreed the Liberty Canyon location was the best option to reconnect this vital corridor and an overpass the best solution.

In 2018, the environmental document was released with a 30% design plan developed by Caltrans and the Resource Conservation District of the Santa Monica Mountains. Since none of the project partners had designed or built a wildlife crossing of this scale and magnitude, in order to ensure the design and engineering of this landmark crossing was guided by the best available science we consulted with some of the world’s foremost experts on wildlife connectivity and crossing structures.

In 2019, we began collaborating with ARC-Animal Road Crossings, an interdisciplinary partnership working to facilitate new thinking, methods, materials and solutions for wildlife crossing structures. In May of 2019, the National Wildlife Federation hosted ARC and its partner the Ecological Design Lab, to conduct an integrated design workshop for project partners, key stakeholders, local residents, scientists, elected officials, and members of the Native American community. In June of 2021, ARC also conducted an additional technical review at the 95% designed milestone.

As a recommendation from the 2019 workshop, the partners conducted a RFP process and selected a world-renowned team led by a landscape architectural practice, Living Habitats LLC, to provide a design guidance report for the final design and engineering stage of the project—they produced an extensive 200-page book, “Designing for Wildlife: Strategies and Considerations for the Wildlife Crossing at Liberty Canyon,” which helps guide design decisions for the project team. Using a science-based strategy and an integrated design approach, Living Habitats has been working with Caltrans and the project partners on every aspect of the design planning process and is also helping to monitor construction.

The main crossing structure will be 210-foot-long across the freeway, and scale 170 feet in width along the freeway, and will be 10 – 12 acres in total—roughly the size of an American football field!

Once built, it will be the largest wildlife crossing in the world of its kind. There are some nuances to how you define that, but that is the phrase we have fact checked. It is also the first to be done of this scale in an urban area.

It will span ten lanes of pavement, or eight lanes of traffic. So, both numbers are correct. The other two lanes are breakdown lanes. Caltrans uses the “ten lanes of pavement” to denote traffic plus breakdown lanes.

As part of the feasibility study, planning and environmental review for our project, a tunnel was eliminated from consideration as a solution as it does not provide for a fully connected ecosystem and not all wildlife will use a tunnel. The goal of the Liberty Canyon crossing is to reconnect an entire ecosystem in the middle of one of the world’s biodiversity hotspots, and allow for connectivity of flora and fauna, as well as save the local mountain lion population.

A tunnel would also have been more expensive given some original Caltrans estimates, as you cannot drill the needed size given the distance, and Caltrans would have had to perform a “cut and cover,” which uses excavation equipment to dig a trench and then cover it with concrete. To do this would have required the 101 Freeway—one of the busiest freeways in the world—to close for a period of time. We think everyone in the Los Angeles area would agree this isn’t feasible nor desirable!

We lead with the science. We are not trying to build the world’s largest wildlife crossing because we want to be ambitious, we have to build the largest in the world because that’s what the project requires to be successful. We would gladly build the smallest crossing in the world, yet we don’t have the ability to shrink the 101 Freeway. What first and foremost dictates the size of the crossing is it has to cover ten lanes of pavement over the 101, along with Agoura Road. Crossing science also has shown that for every foot long a crossing needs to be, the width needs to increase to make the landscape appear inviting to wildlife—a narrow passageway across the freeway would deter animal movement.

Crossings have different factors that drive design, and are all site specific, and the Liberty Canyon crossing is not comparable with others. Factors that drive our design are things like the slope at our location, the size of the freeway, the urban setting and traffic.

For example, many existing wildlife crossings are located in areas with average traffic of less than 10,000 cars per day. Parleys Summit receives an average of 10,000 cars per day. Liberty Canyon gets over 300,000 cars a day and is one of the busiest roadways in the world. We have to mitigate for impacts others do not, like extensive sound and light pollution, which influences the design. We have to add sound walls for example, where other crossings might not have such considerations.

We also have only one site where we can location this crossing—it’s the last 1,600 feet with protected space on both sides of the freeway in the area, and this site, from an engineering and design perspective, is not ideal and requires additional considerations that also add to the cost like grading and sloping. We also have to relocate utilities, which increases the expense as well.

Additionally, most other crossings are trying to solve a roadkill problem. Parleys Summit was nicknamed “slaughter alley,” for example, because of the excessive number of wildlife-vehicle collisions. By contrast, we do not receive a comparable amount of animal deaths at Liberty Canyon given most animals abandon attempts to cross given the formidable barrier the 101 presents. Our main project goal is reconnecting an entire ecosystem, for both flora and fauna, to solve for genetic isolation and to prevent the extinction of a mountain lion population, which requires a biological focused design rather than one just developed for conveyance. And this contributes to design, scope and cost—for example, just adding the needed soil base alone to create a living habitat adds significantly to the load requirements for the structure.

Unlike a traditional freeway overpass, the crossing will support wildlife and provide the habitat, shelter, food and water that individual species need to thrive. To achieve this, the top of the structure will be covered in nearly one acre of native vegetation. The wildlife crossing will connect native chaparral and coastal sage scrub to the north and south by providing an addition of over ten acres of habitat restored as coastal sage scrub and oak savannah.

Yes! With the help of Caltrans and the National Park Service, Living Habitats started collecting seeds, acorns and mushrooms over a year ago. In 2022, a special project nursery was built, where much of the plants will be grown. These will be planted on the site allowing the habitat to grow vegetation naturally throughout the site from the soil up and retaining the critical local genetic material. Native oak and willow trees sourced from the site will also be planted and ten acres of space along the two adjoining slopes where the wildlife crossing will be built, will also be improved.

We are also restoring the native vegetative community to a project site that has experienced both a reduction in biodiversity as well the onslaught of non-native vegetation that represents an increase in the potential fuel load for future wildfire. These invasive species are being removed within the project footprint and are being replaced with an array of native species, restoring and improving the health of the ecosystem. In addition, the project includes cutting-edge solutions for restoring biological health to the soils on the site through the collection of mycorrhizal fungi and the preparation of native inoculum for reintroduction into the constructed landscape.
The site grading and vegetative strategies will replace several acres of invasive grasses and will serve to improve the overall health of the ecosystem as well as protect against surface erosion and impacts to the existing waterways.

During the public engagement process, the community heavily supported planning that would allow wildlife every opportunity for safe passage, and it was decided that there would be no trails or public access. However, the crossing will be seen along the recreation trails that are in the area, and a viewing platform will be built to facilitate optimal viewing, too.

We have consulted with fire officials, (and fire safety is a part of any Caltrans project) and have been advised the wildlife crossing poses no additional risk in terms of wildfire spread. Fire can easily jump a half a mile or more, indeed, the Woolsey Fire crossed the 101 Freeway right at the crossing location and burned the entire site, demonstrating you don’t need the crossing for a fire to jump the freeway.
The crossing project will actually help with fire safety as we are restoring native vegetation on and around the crossing—currently, the project area is mostly non-native mustard, a plant that poses more of a fire risk than native grasses. And on the south side, we funded the undergrounding of electrical transmission lines, which also reduces fire risk.

“This is a huge step forward. Not only will Liberty Crossing be the largest wildlife crossing of its kind in the world, it is emblematic of the bold and creative solutions we need to protect California’s wildlife as our state continues to grow. Nature-based solutions like Liberty Crossing are also essential for combatting the climate crisis and our work to conserve 30 percent of California’s land and coastal waters by 2030.”
Wade Crowfoot, California Secretary for Natural Resources

The wildlife crossing will connect native chaparral and coastal sage scrub habitat to the north and south of the 101 Freeway by providing an addition of over ten acres of habitat. As climate change brings additional pressures to California and the Santa Monica Mountains, both flora and fauna require options in order to persist and adapt to rapidly changing conditions. Reconnecting an ecosystem long fragmented will significantly help mitigate the increasing challenges wildlife and plants face with from a changing climate.

The South Coast Wildlands 2008 whitepaper and the California Department of Fish & Wildlife 2010 California Essential Habitat Connectivity Project have both identified the need to preserve and enhance this critical linkage, “as one of the highest priority linkages to conserve in order to sustain ecological and evolutionary processes” in California’s South Coast Ecoregion, due to existing land use pressures and climate change. The wildlife crossing will also add native vegetation to the landscape, which will help reduce greenhouse gases. In addition, the preservation of biodiversity in the Santa Monica Mountains will reduce greenhouse gases by maintaining substantial, healthy vegetative cover in this area.

“The Wallis Annenberg Wildlife Crossing bridges landscapes, boundaries and disciplines: it is a project of hope that connects people to nature with new, innovative infrastructure, and integrates engineering, ecology and landscape architecture for a sustainable future. In doing so, the Crossing catalyzes a system to reweave California’s significant, biodiverse and
protected landscapes, for people and wildlife — and sets a new standard for reconnecting landscapes worldwide.”
Nina-Marie Lister, Professor & Director, Ecological Design Lab at Ryerson University & ARC Partner

“To break ground for the Wallis Annenberg Wildlife crossing is to launch an exciting new class of green infrastructure for biodiversity. Not only will it cross one of the largest and busiest highways in North America, but it will do so with close attention and respect to the protected landscapes on each side of the highway that ensure its success. Its design is the ideal blend of structural and natural design and it will serve not just as a crossing for wildlife but as an inspiration to the world that we can build well for nature and our shared future.”
Jeremy Guth, Conservation Director, the Woodcock Foundation & Founding Partner and Steering Committee Member, ARC Solutions

Indeed, wildlife crossings are nothing new, and the Wallis Annenberg Wildlife Crossing benefited from decades of science, design and experience from crossings around the world. Yet it is also a landmark crossing in many ways, such as the densely populated location, the unprecedented research, the project goal of saving a population of animals threatened with extinction and reconnecting a regional ecosystem, the integrated design, and the significant public-private partnership.

The Wallis Annenberg Wildlife Crossing is the first to attempt such a large-scale intervention for wildlife in such an urban setting — the greater Los Angeles metropolitan area is the most densely populated area in the United States and is home to 20 million people.

The National Park Service research that led to discovering the need for the crossing is groundbreaking as well—thought to be one of the longest running studies of urban carnivores. Since 1996, NPS biologists have researched carnivores and other local wildlife in the Santa Monica Mountains and the surrounding region. The project began right in the Liberty Canyon area, with the tracking of bobcats and coyotes, and it expanded to include mountain lions in 2002. Overall, the research has focused on urbanization and habitat fragmentation in wildlife communities. The study will continue to provide landmark science for urban wildlife conservation that will help inform future efforts worldwide.

Additionally, the project goals differ from many other crossings, which are trying to solve a roadkill problem. By contrast, Liberty Canyon is not the site of as significant an amount of animal deaths by vehicles as other projects, as most animals abandon attempts to cross given the formidable barrier the 101 presents. Our main project goal is reconnecting an entire ecosystem, for both flora and fauna, to solve for genetic isolation and to prevent the extinction of a mountain lion population, which requires a biological focused design rather than one just developed for conveyance. The 101 Freeway isolated the entire Santa Monica Mountains from the rest of the world for the first time in its evolutionary history. We can find no precedent of a crossing designed to reconnect an entire regional ecological system.

The design reflects a wholescale ecosystem approach, which is also not typical for the majority of crossings. While the physical bridging structures serve as the keystone element, the full project embraces a comprehensive design solution that leverages multiple facets of scientific research, sustainable principles, and best practices in support of an ecologically vibrant and resilient solution for regional habitat connectivity. As the team at ARC: Animal Road Crossings, wrote as part of their technical design review in 2021:

“Where this project really excels, is the treatment of the landscape surface as a set of specifically designed and integrated ecosystem types that reflect the native plant communities and habitats that create a draw for the target species. In this way, it’s critical to appreciate that the landscape surface is not “surface decoration” or an add-on, but rather is integral to the ecological functioning of the crossing design as a system – and to its success.

This project area extends far beyond the crossing overpass structure, encompassing an
ecological design effort impacting eight acres of the surrounding landscape. The scale and magnitude of this endeavor should be highlighted as it further emphasizes the singular and extraordinary nature of the Liberty Canyon project in advancing connectivity and wildlife conservation across urbanized landscapes.”

The Wallis Annenberg Wildlife Crossing is a public-private partnership of monumental scope that has leveraged the expertise and leadership of dozens of organizations and institutions from across the state, country, and the world. The work of the Liberty Wildlife Corridor Partnership serves as an international model for collaborative solutions for wildlife in the transportation sector, including the role of private philanthropy. The invaluable contribution of Wallis Annenberg and the Annenberg Foundation in bringing their leadership in philanthropy to this project cannot be overstated. Their donation of $26 million dollars—the largest private contribution to a wildlife crossing to date—helped us leverage public funds and inspired the additional giving needed to reach the finish line.

The Wallis Annenberg Wildlife Crossing is also inspiring efforts to improve connectivity across California, the United States and the world. As Louis Sahagún wrote in an article about the crossing for the Los Angeles Times, “Future historians may look back on the second decade or so of 21st century American architecture as the Age of Wildlife Crossings. Congress in November passed a national infrastructure package that for the first time sets aside $350 million in federal funding for wildlife crossings to reduce wildlife-vehicle collisions in all 50 states.”

“Wildlife crossings restore ecosystems that had been fractured and disrupted. They reconnect lands and species that are aching to be whole. I believe these crossings go beyond mere conservation, toward a kind of environmental rejuvenation that is long overdue. It’s a model for the kind of public-private partnerships that can heal our environment for the long haul. Thanks to this extraordinary commitment, California is now in the vanguard of that change.”
Wallis Annenberg, Chairman, President, and CEO of Annenberg Foundation